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Re: PATCH: Add memory barrier to malloc
On Sun, May 04, 2003 at 09:03:38AM -0700, Dan Kegel wrote:
> Momchil Velikov wrote:
> >>>>>>"H.J. Lu" == H J Lu <hjl@lucon.org> writes:
> >
> > H.J. Lu> --- libc/malloc/arena.c.barrier 2002-12-26 16:36:41.000000000 -0800
> > H.J. Lu> +++ libc/malloc/arena.c 2003-05-03 23:56:59.000000000 -0700
> > H.J. Lu> @@ -758,6 +758,7 @@ arena_get2(a_tsd, size) mstate a_tsd; si
> > H.J. Lu> /* Add the new arena to the global list. */
> > H.J. Lu> (void)mutex_lock(&list_lock);
> > H.J. Lu> a->next = main_arena.next;
> > H.J. Lu> + atomic_write_barrier ();
> > H.J. Lu> main_arena.next = a;
> > H.J. Lu> (void)mutex_unlock(&list_lock);
> >
> > Why would a barrier be needed inside a critical section ? Aren't POSIX
> > memory model guarantees sufficient ?
>
> I guess list_lock doesn't protect accesses to main_arena?
That is currect. list_lock isn't held when walking through linked list
for available arenas.
H.J.